The present invention relates to a deflection system for a cathode-ray tube, particularly to a deflection system for enabling a decrease of ringing.
According to conventional devices of this type, as described in Japanese Patent Laid Open No. 34549/83, first and second resistors are respectively connected between a central connection point of a deflecting coil wound in a toroidal fashion around a core between winding start and end points of the coil, and the resonance of a resonance circuit formed by a deflection system and a floating capacity induced between lines of winding layers of the toroidally wound deflecting coil is damped to reduce ringing which causes light and dark stripes in a reproduced image reproduced on a cathode-ray tube simultaneously with the above resonance.
Referring to FIG. 1, there is illustrated a conventional winding method for a conventional vertical deflecting coil, in which the ordinate represents the number of each winding layer, while the abscissa represents the angle .theta. of each winding. In the figure, 1 represents a first layer, a second layer, 2 . . . and 5 a fifth layer. A vertical axis 6 extends through the center of the vertical deflecting coil. According to the winding method shown in FIG. 1, the winding for layer 1 starts from a winding start point 10 at a -70.degree. point and ends at +70.degree. point with return being made to the -70.degree. point using a return line 12 (indicated by a dotted line). The second-layer 2 winding starts from the -70.degree. point and ends at the +70.degree. point with a return being made to a -50.degree. point. Then a third-layer 3 winding starts from the -50.degree. point and ends at the +50.degree. point, with return being made to the -50.degree. point. The fourth-layer 4 winding also starts from the -50.degree. point and ends at the +50.degree. point with return being made to a -30.degree. point; and a fifth-layer 5 winding starts from the 30.degree. point and ends at a winding end point 14 at a +30.degree. point. Thus, in the winding method shown in FIG. 1, all the winding layers are approximately symmetric with respect to the vertical axis 6.
FIG. 2 illustrates the distribution of induced voltages from a horizontal deflecting coil relative to the vertical deflecting coil wound according to the winding method shown in FIG. 1. In FIG. 2, a normalized induced voltage distribution curve of the first and second layers 1 and 2 exhibits an increase from 0.degree. at the -70.degree. point with respect to the vertical axis 6 and reaches a maximum at the 0.degree. point, and after passing the 0.degree. point, exhibits a decrease until becoming 0.degree. at +70.degree. point. The reason why a change is made from increase to decrease at the 0.degree. point is because the voltage induced in the coil of a small number of windings is inverted in polarity between positive and negative sides of angle .theta. with respect to 0.degree. as a boundary. An induced voltage distribution of the third and fourth layers 3 and 4 increases from 0.degree. at the -50.degree. point and reaches a maximum at the 0.degree. point, then after passing the 0.degree. point, it decreases until it becomes 0.degree. at the +50.degree. point. The induced voltage distribution of the fifth layer 5 increases from 0.degree. at the -30.degree. point and reaches a maximum at the 0.degree. point, then after passing the 0.degree. point, it decreases until it becomes 0.degree. at the +30.degree. point.
In FIG. 2, the induced voltage at the winding start point of the coil is assumed to be 0.degree. and differences are developed in the following relation among the induced voltage of the first and second layers, induced voltage of the third and fourth layers, and induced voltage of the fifth layer: (1st and 2nd layer induced voltage)&gt;(3rd and 4th layer induced voltage)&gt;(5th layer induced voltage). This relation is valid on the condition that the winding pitch (rad/turn) is constant and that all the winding layers are approximately symmetric with respect to the vertical axis 6.
In the winding method shown in FIG. 1, as mentioned above, there is developed a voltage difference of [(1st and 2nd layer induced voltage)-(3rd and 4th layer induced voltage)], i.e., an inter-layer voltage difference 8.
On the other hand, FIG. 3 is an electrical equivalent circuit diagram of a deflection system related to a ringing phenomenon which ringing is generated in the deflection system. In FIG. 3, there is shown a deflection system 1 including a horizontal deflection coil 2 supplied with power from a horizontal deflection circuit 2' and a vertical deflection coil 3 magnetically coupled with the horizontal deflection coil. Only half of the upper and lower portions of the vertical deflection coil is illustrated in FIG. 3, and a connection circuit to a vertical deflection circuit is omitted because it has nothing to do with the occurrence of ringing. The vertical deflection coil 3 is divided into a negative-side coil 3a and a positive-side coil 3b, with angle .theta., on both sides of the vertical axis 6. The coils 3a and 3b are magnetically coupled to the horizontal deflection coil 2 (supplied with electric power from the horizontal deflection circuit 2') so as to be opposite in polarity to each other. Since the winding layers of the vertical deflecting coil 3 are stacked successively, an inter-layer floating capacity 9 is present between adjacent winding layers. Between the winding layers which are different in winding start angle from each other, there occurs the inter-layer potential difference 8 corresponding to only an induced voltage which varies in such angular range. Consequently, a voltage corresponding to the inter-layer potential difference 8 is developed relative to the inter-layer floating capacity 9 developed between adjacent winding layers of the vertical deflecting coil 3, thus causing resonance, and hence the occurrence of ringing. As to the ringing phenomenon generated in the deflection system, ringing caused by the inter-layer floating capacity 9 of the vertical deflection coil is more predominant than ringing caused by an inter-line floating capacity of the winding layers. Heretofore, no consideration has been given to decreasing the ringing caused by the inter-layer floating capacity 9. Additionally, a satisfactory ringing diminishing effect is not obtained in the case of a high horizontal deflection frequency. In the prior art, moreover, since a damping resistor is used, the working efficiency is poor and the manufacturing cost increases.